Sorry about the late notice, but I'm seeing what looks like a regression in the Rosegarden trunk. It's easy to reproduce--start a new composition, draw a segment of any length, and try to open it in the notation editor using any of the three available methods (double-click, toolbar button, or menu). Rosegarden will promptly abort. If it was run from the console, you'll see this message in the last line of output: "QWidget::setMinimumSize: (/Rosegarden::HeadersGroup) Negative sizes (-1,0) are not possible".
Can anyone confirm if this is a bug outside of my own box? If so, I can probably try to bisect it this weekend.